In focal i386 architecture is missing

see https://discourse.ubuntu.com/t/intel-32bit-packages-on-ubuntu-from-19-10-onwards/11263 and the pages linked from there.

Thanks for the answer. I admittedly only cross read the thread but I still don't get why it is only missing from focal (cf. https://packages.ubuntu.com/search?suite=all&searchon=names&keywords=libdeflate0) :
Package libdeflate0

    focal (20.04LTS) (libs): fast, whole-buffer DEFLATE-based compression and decompression [universe]
    1.5-3: amd64 arm64 armhf ppc64el s390x
    impish (21.10) (libs): fast, whole-buffer DEFLATE-based compression and decompression
    1.7-2ubuntu2: amd64 arm64 armhf i386 ppc64el s390x
    jammy (22.04LTS) (libs): fast, whole-buffer DEFLATE-based compression and decompression
    1.10-2: amd64 arm64 armhf i386 ppc64el s390x
    kinetic (libs): fast, whole-buffer DEFLATE-based compression and decompression
    1.12-1: amd64 arm64 armhf i386 ppc64el s390x

If the package is only missing from focal, but is available in jammy and kinetic (I confess that I did not verify that before), then my answer is only party applicable.
In the process of removing the i386 architecture it was decided to keep selected libraries also in their 32bit variant (e.g. to support wine, steam and similar programs). It seems that libdeflate was not in that list in the first step and has been added only later, perhaps together with re-allocating it from "universe" to "main".

I do not see a short-term solution except eventually:
- searching for a PPA that has such version (if existing at all)
- trying to manually install the version for a later Ubuntu release (may be complicated because of missing dependencies)
- upgrading to a newer Ubuntu release (e.g. 22.04 jammy).